Armed police have evacuated part of central London amid reports of gunshots in Oxford Street and Oxford Circus Tube station.
Police say they are responding “as if the incident is terrorist related” but have not yet located any casualties.
“Armed and unarmed officers are on scene and dealing along with colleagues from British Transport Police (BTP),” a spokesperson for the Metropolitan Police said.
“If you are on Oxford Street go into a building and stay inside until further direction. Avoid travelling to the Oxford Street area.”
Ryan Butcher, who was inside the station at the time, said passengers were told to evacuate the station in a tannoy announcement saying there had been a “reported emergency”.
He had reached street level when panic broke out and people started running.
“I just heard screams, someone shouted ‘run,” he added. “I saw smoke…people started falling over in the streets.
“I saw everyone running into buildings so I went into the nearest one.”
Mr Butcher was sheltering in a nearby restaurant, where he said other people were “shaking and crying”, adding: “It’s just terrifying.”
He has since been allowed to leave by police officers, who are directing members of the public away from the area.
Police were first called at 4.38pm, with the incident coming as shoppers flocked to central London on Black Friday.